我有JPanel的按钮，按下时应该将我发送到另一个屏幕，但是我一直收到错误。我试过谷歌搜索它，但没有任何关于它的信息。
完整代码
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JLabel;
import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.Popup;
import javax.swing.JOptionPane;
import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.FlowLayout;
import javax.swing.JRadioButton;
import javax.swing.JPasswordField;
import javax.swing.ButtonGroup;//to put radio buttons together
public class Graphics extends JFrame {//this class is to display the GUI on the screen
private JButton enter;//enter on login
private JButton exit; //exit program
private JButton button1; //enter on menu
private JButton button2; //enter on withdraw
private JButton button3; //enter on deposit
private JButton back;//button to return to main menu from other options
private JRadioButton balance; //menu for operation selection
private JRadioButton withdraw;
private JRadioButton deposit;
private ButtonGroup buttonMenu;//to put radio buttons together
private JTextField loginBox; //to enter username
private JPasswordField password;
private JTextField input1;//to enter withdraw amount
private JTextField input2;//deposit amount
private JPanel loginPanel;//first screen
private JPanel menuPanel;
private JPanel withdrawPanel;
private JPanel depositPanel;
private JPanel balancePanel;
private JPanel setPanel; //to hold the other panels
private CardLayout cl;//to set the different panels
private int login1;
private int password1;
private double login2;
private double password2;
ATM atmObject = new ATM();
public Graphics(){ //constructor
super("My ATM");
//ATM object = new ATM();//object to call methods in ATM
//to access information stored
CardLayout cl = new CardLayout();
setPanel = new JPanel();//panel to store the other panels
setPanel.setLayout(cl);//create the different set of windows
/***define and initialize all buttons, labels etc.***/
JLabel login = new JLabel("Login"); //to put next to login field
JLabel passcode = new JLabel("Password");
loginBox = new JTextField(6);//to enter login
password = new JPasswordField(6);//to enter password
input1 = new JTextField(6);
input2 = new JTextField(6);
enter = new JButton("Enter");
back = new JButton("GO Back");
exit = new JButton("Exit");
button1 = new JButton("Enter");//button for main menu
button2 = new JButton("Enter");//button for withdraw
button3 = new JButton("Enter");//button for deposit
balance = new JRadioButton("balance inquiry", false);//menu for operation selection
withdraw = new JRadioButton("withdraw from account", false);
deposit = new JRadioButton("deposit to account", false);
/***end of definitions***/
/*****set-up login screen****/
loginPanel = new JPanel();
loginPanel.add(login);//label
loginPanel.add(loginBox);//textbox
loginPanel.add(passcode);//label
loginPanel.add(password);//input password
loginPanel.add(enter);
loginPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
setPanel.add(loginPanel, "LoginScreen");//add login screen to panel and set
//items orientation to the left
//here add code to check password on file
//obtain password as set of characters
//int cool = Integer.parseInt(loginBox.getText()); in a single step
//String inputA = loginBox.getText();//obtain input from user as a string
//JTextField inputB = new JTextField();
//login1 = Integer.parseInt(inputA); //convert it to int so it can be used
//char[] passcode2 = password.getPassword(); //create array of chars to get password
//password1 = Integer.parseInt(String.valueOf(passcode2));//changing characters to int
/****setup main menu***/
menuPanel = new JPanel();
buttonMenu = new ButtonGroup();
menuPanel.add(balance);
menuPanel.add(withdraw);
menuPanel.add(deposit);
//make all radio buttons connected
buttonMenu.add(balance);
buttonMenu.add(withdraw);
buttonMenu.add(deposit);
menuPanel.add(button1);//add entebr button
menuPanel.add(exit);
menuPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
setPanel.add(menuPanel, "MainMenu");//add window to display
/***setup balance inquiry screen***/
balancePanel = new JPanel();
JLabel balance = new JLabel("the balance in your account is :");
JTextField balanceDisplay = new JTextField(5);//to display balance
balanceDisplay.setEditable(false);
//here code to call balance from ATM
balancePanel.add(balance);
balancePanel.add(balanceDisplay);
balancePanel.add(back);
balancePanel.add(exit);
balancePanel.setLayout(new FlowLayout(FlowLayout.LEFT));
setPanel.add(balancePanel, "Blance");//add window to display
/**end of balance inquiry**/
/****setup screen to withdraw money***/
withdrawPanel = new JPanel();
JLabel message = new JLabel("enter amount to withdraw");
withdrawPanel.add(message);//display message
withdrawPanel.add(input1);
withdrawPanel.add(button2);
withdrawPanel.add(back);
withdrawPanel.add(exit);
withdrawPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
//here code to call method to withdraw money
setPanel.add(withdrawPanel);//add window to display
/***setup screen to deposit***/
depositPanel = new JPanel();
JLabel message2 = new JLabel("Enter amount to deposit");
depositPanel.add(message2);
depositPanel.add(input2);
depositPanel.add(back);
depositPanel.add(exit);
depositPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
setPanel.add(depositPanel, "Deposit");
/***end deposit panel***/
getContentPane().add(setPanel);
//create event handler and make buttons events
theHandler handler = new theHandler();//builds an action listener object
enter.addActionListener(handler);
exit.addActionListener(handler);
back.addActionListener(handler);
button1.addActionListener(handler);
button2.addActionListener(handler);
button3.addActionListener(handler);
//add the frame to the window
//boolean access = atmObject.Info(id, password1);
//int i;
// if(access == true){
//enter.addActionListener(handler);//if login is correct call the event handler
}
//class inside class
//inner class inherits everything from outer class
private class theHandler implements ActionListener{//this class handles the events
//waits for an event to happen and execute the code
public void actionPerformed(ActionEvent event){//actionPerformed is a built-in method
//ActionEvent is also built-in
//String string = "";
boolean info = false;//to check if the login and password are correct
if(event.getSource()== enter){//getSource = where the event occurred
JOptionPane.showMessageDialog(null, "Hello");
//String inputA = loginBox.getText();//obtain input from user as a string
// login1 = Integer.parseInt(inputA); //convert it to int so it can be used
//char[] passcode2 = password.getPassword(); //create array of chars to get password
//password1 = Integer.parseInt(String.valueOf(passcode2));//changing characters to int
//info = atmObject.Info(login1, password1);
// if(info==true)
cl.show(setPanel, "MainMenu");
}
}
}
我放置弹出窗口以查看按钮是否有问题，但弹出窗口显示按下按钮的时间。因此事件处理适用于按钮。我按下按钮时收到的消息。
Graphics$theHandler.actionPerformed
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
就是这样。我有另一个程序的类似代码，但它没有给我任何错误。为什么说未知来源？
这是我的主要课程
import javax.swing.JFrame;
public class Display {//this class is to call the other methods
public static void main(String[] args) {
Graphics atmObject = new Graphics();
atmObject.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
atmObject.setSize(350, 100);
atmObject.setVisible(true);
}
}
我有另一个类，但是我还没有在我的代码中使用它。我为我的其他ATM类创建了一个对象，但它还没有在代码中使用，所以它不应该干扰代码。
答案 0 :(得分：1)
如果没有更多信息，就不可能100％，但我相信你正在掩盖你的变数。
我的假设基于以下内容......
// Here, you create a local copy of the CardLayout
CardLayout cl = new CardLayout();
// But here it seems you are creating a class instance of the setPanel...
setPanel = new JPanel();//panel to store the other panels
setPanel.setLayout(cl);//create the different set of windows
JButton enter = new JButton("Enter");
JPanel loginPanel = new JPanel();
loginPanel.add(enter);
和...
// You create a instance of some handler (presumably a implementation of ActionListener)
// which suggests that the handler is not (at least) an anonymous inner class...
theHandler handler = new theHandler();//builds an action listener object
enter.addActionListener(handler)
loginPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
setPanel.add(loginPanel, "LoginScreen");
最后......
if(event.getSource()== enter){//getSource = where the event occurred
JOptionPane.showMessageDialog(null, "Hello");
// You can reference "cl", which suggests that the program
// can compile, meaning the "cl" must be declared some where
// and based on the method you are accessing, is probably
// a CardLayout...which hasn't being initialised...
cl.show(setPanel, "MainMenu"); <-----here is the problem
根据整个代码进行更新
好的，在您Graphics课程中，您声明cl类型为CardLayout的实例变量....
public class Graphics extends JFrame {//this class is to display the GUI on the screen
/*...*/
private CardLayout cl;//to set the different panels
然后在你的构造函数中......
public Graphics(){ //constructor
/*...*/
CardLayout cl = new CardLayout();
您正在声明它...这意味着构造函数中的cl仅在构造函数中有效且可行。一旦构造函数存在，引用就不再有效。这使实例变量cl未初始化... OR null
然后......在您的actionPerformed方法中，您引用了cl的实例变量null ...
private class theHandler implements ActionListener{//this class handles the events
//waits for an event to happen and execute the code
public void actionPerformed(ActionEvent event){//actionPerformed is a built-in method
//ActionEvent is also built-in
/*...*/
// Then you try and reference the instance variable which is null
cl.show(setPanel, "MainMenu");
}
}
在构造函数中，更改...
CardLayout cl = new CardLayout();
要...
cl = new CardLayout();
也...
Graphics已经是java.awt中定义的类。我强烈建议您不要自己使用它，因为从长远来看它只会让您和其他人感到困惑...... 答案 1 :(得分：1)
Graphics$theHandler.actionPerformed
类名应以大写字母开头。 “theHandler”应该是“TheHandler”（实际上它应该是一个更好的描述性名称）。
看起来您的班级名称是“图形”。这已经是JDK类名。使用其他名称。
怀疑这些建议将解决您的问题。为此，我们需要SSCCE。